1. Field of the Invention
The present invention relates to a transmitting and receiving apparatus which uses a frequency division multiple access (FDMA) system for a multiple access system and a time division duplex (TDD) system for a bidirectional communication system. Particularly, it relates to a high frequency circuit block of a mobile station (hand set) or a base station (base unit) in that system.
2. Description of the Related Art
A transmitting and receiving apparatus such as a digital cordless telephone or the like employing a CT-2 system which is widely adopted in Europe, etc. uses the FDMA system for the multiple access system and uses the TDD system for the duplex system.
A system for connecting to a specified destination of communication in a communication space which is simultaneously utilized by a plurality of users is called multiple access. The CT-2 system employs the FDMA system for the multiple access. In the FDMA system, one frequency is allocated to each user.
The CT-2 system employs the TDD system (one-frequency time-division bidirectional communication system) as a system for separating a channel (reception channel) from a base station (base unit) to a mobile station (hand set) and a channel (transmission channel) from a mobile station (hand set) to a base station (base unit).
The TDD is a system in which the same frequency is used alternately for transmission and reception in a time division fashion. For example, transmission and reception both using a carrier signal in one frequency band are alternatively switched at every one millisecond.
Since it has been difficult to form a band-pass filter having a sharp cut-off characteristic in a high-frequency circuit block of a mobile station (hand set) of a FDMA/TDD transmitting and receiving apparatus, the transmitting and receiving apparatus has required a double superheterodyne reception system.